1. Field of the Invention
This invention relates to a drum rotation indicator. More specifically, it concerns such an indicator, for use in a crane, to enable the crane operator to physically sense linear movement of a cable, that has one end wound about a drum and another end attached to a gripping implement, when neither end of the cable can be seen by the crane operator without distracting his attention from a signal man.
2. Description of the Prior Art
Drum rotation indicators have been used to detect motion of a hoist drum in a crane, as shown in the U.S. Pat. Nos. 2,717,993; 2,745,633 and 2,776,814. All of these patents show feel type indicators that are driven by a rotary cable with motion being taken from a hoist drum. Among the problems associated with rotary cable driven indicators are difficulty in turning the unit off when not in use and inaccuracy in reading the unit due to wind-up of the cable immediately after being turned on.
In addition to the rotary cable and feel type indicator shown in U.S. Pat. No. 2,717,993, this patent also shows a light or buzzer that can be actuated by rotation of a cam, which engages a pin of a make and break switch, thus causing the contacts to make and break on each rotation of the cam. In this patent, the cam rotates with the cable, but such an indicator cam could be mounted to rotate with the drum. Electrical units are known, to have a roller switch riding on a cam or a proximity switch sensing gear teeth, to produce electrical signals, that are usually transformed to either a beeping horn or to mechanical pulses created by a solenoid. These electrical units require a manual ON-OFF control. The switch mechanism usually runs all the time, thus reducing the switch life. The electrical circuitry often makes trouble shooting more difficult than mechanical units. Sound units, such as a beeping horn or a buzzer, are not accepted by some equipment operators because of irritable horn noise. Mechanical pulsating units of the solenoid type usually give weak signals to the operator.
U.S. Pat. No. 1,467,373 shows an apparatus for measuring the extent of vibration of a shaft within its bearing. This apparatus includes a vibratory needle that is slidably carried by a standard. The needle is resiliently urged from the standard, in a radial direction towards the shaft, to contact the shaft with a bearing foot, that is carried at one end of the needle, and an indicator knob is mounted at the other end of the needle, so that, any vibrations of the shaft can be readily determined by observing the knob.